The present invention relates to electrophotographic developing apparatus and more particularly to devices in such apparatus for mixing the developer powder.
Upon development of electrostatic latent images formed on a light sensitive surface in electrophotographic apparatus, such as electrostatic development machines, it is generally necessary to render the supply of the developer uniform over the entire surface of the developing station. However, where electrostatic latent images formed on the light sensitive surface are present with a lateral deviation of images on the developing surface, the developer on the developing roll is consumed with a deviation in the axial direction of the roll corresponding to the deviation present in the elcetrostatic latent images. Accordingly, the amount of the developer transported by the developing roll is gradually decreased in the portion corresponding to the electrostatic latent images requiring the larger amount of developer. Efforts have therefore been made to incorporate mixing devices in the developing apparatus to restore a uniform supply of developer across the width of the developing station.
One conventional mixing device utilizes assemblies of mixing chutes diverting the developer at slight angles in one assembly of chutes and then in the opposite directions in a second assembly of chutes. Such assemblies may include parallel chutes on both sides of the centerline of the developing station, the chutes on each side being at different angles, but such assemblies do not significantly intermix the developer across the centerline.
Another conventional mixing device employs rotative screw blades across the width of the mixing station. Ordinarily two such screw blades are positioned in consecutive order, the screws rotating in opposite directions with their axes parallel to the developing and transport rolls. In such screw-mixing devices, however, the developer is forcibly transported in the screw blades. Frictional resistance develops between the developer particles themselves, and between the developer particles and the screw blades, resulting in increased fatigue in the developer.
Such fatigue is particularly significant in developers consisting of toner and resin-coated-iron powder in admixture, wherein the fatigue in the resin-coated-iron powder decreases the length of life of the developer.